3. If you haven’t enabled root storage, slide out the left-hand panel and tap the settings gear icon.

4. Scroll to the bottom and enable “Show root storage.”

5. Exit settings.

6. Slide out the left-hand navigation panel and tap Root.
Scroll down and tap System.

7. Scroll down and tap “build.prop”

8. Open the file using SE Text Editor.

9. Find the line that reads ro.product.model=[YOUR DEVICE] and replace it with the following: ro.product.model=Pixel XL
Add the following on its own line: ro.opa.eligible_device=true

10. Save and exit the file.

11. Reboot your device.

Once you’ve rebooted, navigate to the Apps section of your Settings app and find the Google app to clear its data and cache. After the app restarts, you should be able to activate Google Assistant by long-pressing your home button. Congratulations! You have a Pixel-exclusive feature before the phone’s even out.

📌 Method 2 : (Without Root)

1. Install Google Allo app from playstore or download it from below link.

2. Open Google Allo app and register for a new account.

Done! Now you have successfully enabled the Google Assistant in your device.